DE 39 120 14 A1 discloses a method for determining a value for the friction between a road surface and a tire on a vehicle. As the vehicle approaches a driving condition which is dynamically critical in a lateral direction, values are sensed or calculated for its steering angle, travel speed, velocity of angular yaw and lateral acceleration. Using a mathematical reference model of the vehicle, a reference or intended velocity of angular yaw is determined as a function of the steering angle and the travel speed. In addition, a difference is determined between the actual velocity of angular yaw of the vehicle and the reference or intended velocity of angular yaw. As a measure of the value of the friction between the road surface and the tires of the vehicle, the value of the lateral acceleration is determined for which the difference between the actual velocity of angular yaw and the reference or intended velocity of angular yaw starts to rise steeply.
EP 1 627 790 A1 discloses a method for estimating a coefficient of friction. A steering angle and a lateral acceleration are sensed. An estimated value of the coefficient of friction is determined by means of a table. This table provides several ranges for different steering angles and lateral accelerations, to which are assigned several coefficients of friction. Depending on the steering angle which is sensed and the lateral acceleration which is sensed, the associated range in the table is selected and the assigned coefficient of friction is used as the estimated value of the coefficient of friction.